1. Field of the Invention
The present invention relates generally to the field of illumination and lighting systems, and more particularly to fiber optic or optical waveguide light distribution systems.
2. Description of the Related Art
In 1870, British physicist John Tyndall demonstrated that light could be guided within a water jet through the phenomenon of total internal reflection (TIR). Fiber optics or optical fibers are long, thin, flexible fibers of glass, plastic, or other transparent materials through which light is transmitted using TIR. Because of TIR, light admitted at one end of the fiber can travel through the fiber with very low loss, even if the fiber is curved. Fiber optics are one type of optical waveguide which is a more general class of optical transmission element using TIR.
The phenomenon of total internal reflection (TIR) is central to the operation of fiber optics (and other optical waveguides). Light traveling inside the optical fiber center, or core, which strikes the outside surface (interface) at an angle of incidence greater than the "critical angle" is reflected back toward the inside of the fiber substantially without loss (if defects or impurities in the fiber are ignored). Thus, light can be transmitted over long distances by being repeatedly reflected inwardly thousands of times. In order to avoid losses inherent in real world optical fibers through the scattering of light by impurities or defects on the surface of the fiber, the optical fiber core is clad with a glass or other layer having a much lower refractive index (if no cladding material is placed on the core, then the external environment is the clad). The internal reflections then occur at the interface of the high refractive index glass fiber and the lower refractive index cladding. The critical angle A.sub.c above which TIR occurs, measured from the normal to the core/clad interface is determined by the relative refractive indexes of the core and clad (or surrounding environment), i.e. sin A.sub.c =n.sub.clad /n.sub.core. Thus for TIR to occur, the index of the core must be greater than the index of the surrounding material, and the ratio of the indexes defines the range of angles at which TIR will occur.
Communications engineering has exploited the information carrying capacity or bandwidth of optical fibers by creating communication networks and backbones of optical fibers. Fiber optics is the transmission medium of choice for many cutting edge applications, such as the communication systems linking the computers on Boeing's new 777 jumbo jet and the communication system aboard NASA's new Freedom International Space Station.
However, communication engineering is not the only beneficiary of advances in optical fiber technology. It has become clear that future trends in illumination engineering point to an increasing use of fiber optic or optical waveguide light distribution systems for industrial and home lighting applications.
Currently, the major barriers to the widespread application of optical fiber or optical waveguide systems are high cost and low efficiency. If a higher efficiency light distribution system could be devised, the technology would gain a wider acceptance and increased use.
Coupling losses are the major cause of the low efficiency in conventional fiber optic and other optical waveguide illumination systems. Since transmission losses are low, losses in light in a fiber optic illumination system are mainly a function of the coupling efficiency (or inefficiency) between the external light source and the fiber optic or waveguide distribution system. In conventional systems, an optical reflector, lens or other concentrating system focuses or concentrates the light flux from the source onto the interface of the fiber optic system. The primary losses appear at the source/reflector interface and at the optical system interface. This coupling efficiency can typically be on the order of 50-70%. These sources of losses are, therefore, the primary obstacle to overcome if fiber optic or optical waveguide systems are to become widespread in the lighting of interiors.
What is needed, therefore, is a means and a system for overcoming the losses occurring at the source/reflector interface and the coupling losses that occur between the source of light and the fiber optics or the solid light guide distribution system.